Exploring the Structure of Complex Software Designs: An Empirical Study of Open Source and Proprietary Code

by Alan D. MacCormack, John Rusnak, and Carliss Y. Baldwin

Executive Summary —
How does a product's design mirror the organization that develops it, and how does such a dynamic occur? To track the evolution of one design over time, this exploratory study compared software designs developed via different modes of organization-open source versus proprietary development. As it turned out, the architecture of the product developed by a highly distributed team of developers (Linux) was more modular than another product of similar size developed by a co-located team of developers (Mozilla). The study helped reveal potential performance tradeoffs from architectures with different characteristics. Key concepts include:

The value of design is a managerial choice.

There are important, measurable differences in modularity between different software systems of comparable size and function.

Systems may vary dramatically in terms of their robustness to change, and the costs and efficiency of future enhancements.

Author Abstract

This paper reports data from a study that seeks to characterize the differences in design structure between complex software products. We use Design Structure Matrices (DSMs) to map dependencies between the elements of a design and define metrics that allow us to compare the structures of different designs. We use these metrics to compare the architectures of two software products — the Linux operating system and the Mozilla web browser — that were developed via contrasting modes of organization: specifically, open source versus proprietary development. We then track the evolution of Mozilla, paying attention to a purposeful "re-design" effort undertaken with the intention of making the product more "modular." We find significant differences in structure between Linux and the first version of Mozilla, suggesting that Linux had a more modular architecture. Yet we also find that the re-design of Mozilla resulted in an architecture that was significantly more modular than that of its predecessor, and indeed, than that of Linux. Our results, while exploratory, are consistent with a view that different modes of organization are associated with designs that possess different structures. However, they also suggest that purposeful managerial actions can have a significant impact in adapting a design's structure. This latter result is important given recent moves to release proprietary software into the public domain. These moves are likely to fail unless the product possesses an "architecture for participation."